Restore the use of system isnan() that was removed by

check-in [ea748edecb261f2b].  See
[forum:/forumpost/d7c530ac587f59e6|forum thread d7c530ac587f59e6].

FossilOrigin-Name: b3cfe23bec0b95ca673802526704200e2396df715fdded72aa71addd7f47e0e1

manifest

@@ -1,5 +1,5 @@
-C Fix\san\sassertion\sfault\sin\spcache\sintroduced\sby\s[4bc93658aa563f2f]\sand\ndetected\sby\sOSSFuzz.\s\sTest\scase\sin\sTH3.
-D 2021-09-03T18:11:12.688
+C Restore\sthe\suse\sof\ssystem\sisnan()\sthat\swas\sremoved\sby\ncheck-in\s[ea748edecb261f2b].\s\sSee\n[forum:/forumpost/d7c530ac587f59e6|forum\sthread\sd7c530ac587f59e6].
+D 2021-09-06T11:44:19.557
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -614,7 +614,7 @@ F src/trigger.c 3f612ce5f0858b6c23460a3c799d01f408b49b0b29d931d8b8e6fc224a8667de
 F src/update.c 69c4c10bc6873a80c0a77cb578f9fc60ee90003d03f9530bc3370fa24615772d
 F src/upsert.c 8789047a8f0a601ea42fa0256d1ba3190c13746b6ba940fe2d25643a7e991937
 F src/utf.c ee39565f0843775cc2c81135751ddd93eceb91a673ea2c57f61c76f288b041a0
-F src/util.c eafc8cfeb66fdbf8839922d13019b7882f242ac31b383e3451aab7744c54df3e
+F src/util.c 3f27a1eae01c8bbbb8cdef2f26bd8e6a2a7db08106ef7c3dcc990787a5da6e86
 F src/vacuum.c 454973a59fb20bb982efc2df568a098616db6328a0491b6e84e2e07f7333db45
 F src/vdbe.c 39755f468a623af5e805c65a9ad7edb7c45fd78239fd58a319c7db8dfacc302b
 F src/vdbe.h 25dabb25c7e157b84e59260cfb5b466c3ac103ede9f36f4db371332c47601abe
@@ -1922,7 +1922,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P c7b34930e27597e7f634ad76be55fc436dcb84ea48d5b41b5d7f3596285dd672
-R 4f7910f5f5ef11dddc7f6d21ffbd4cd3
+P 2262a49467fa56c386080dac3e99a66e16c1700e138dba74db66e7b93ae76bf5
+R d8ba99d74275c13962c86910c5d71eaf
 U drh
-Z 3eac870735d941254d467d34517d396e
+Z b03f3a58c51480d14c4f0272dcd9a510

manifest.uuid

@@ -1 +1 @@
-2262a49467fa56c386080dac3e99a66e16c1700e138dba74db66e7b93ae76bf5
+b3cfe23bec0b95ca673802526704200e2396df715fdded72aa71addd7f47e0e1

src/util.c

@@ -60,11 +60,21 @@ int sqlite3FaultSim(int iTest){
 #ifndef SQLITE_OMIT_FLOATING_POINT
 /*
 ** Return true if the floating point value is Not a Number (NaN).
+**
+** Use the math library isnan() function if compiled with SQLITE_HAVE_ISNAN.
+** Otherwise, we have our own implementation that works on most systems.
 */
 int sqlite3IsNaN(double x){
+  int rc;   /* The value return */
+#if !SQLITE_HAVE_ISNAN && !HAVE_ISNAN
   u64 y;
   memcpy(&y,&x,sizeof(y));
-  return IsNaN(y);
+  rc = IsNaN(y);
+#else
+  rc = isnan(x);
+#endif /* HAVE_ISNAN */
+  testcase( rc );
+  return rc;
 }
 #endif /* SQLITE_OMIT_FLOATING_POINT */